The invention relates to perpendicular magnetic recording read heads, and more particularly to such a read head having a magnetic shield to reduce side reading.
Longitudinal magnetic recording heads for use with computer hard disc drives are generally known. Longitudinal magnetic recording in its conventional form has been projected to suffer from superparamagnetic instabilities at densities above approximately 40 Gbit/in2. It is believed that reducing or changing the bit cell aspect ratio will extend this limit up to approximately 100 Gbit/in2. However, for recording densities above 100 Gbit/in2, different approaches may likely be necessary to overcome the limitations of longitudinal magnetic recording.
An alternative to longitudinal magnetic recording is perpendicular magnetic recording. Perpendicular magnetic recording is believed to have the capability of extending recording densities beyond the limits of longitudinal magnetic recording due, for example, to use of a thicker recording layer and/or the use of a soft magnetic underlayer. However, a disadvantage of implementing perpendicular magnetic recording is that there is not a generally acceptable perpendicular reader design. As a result, a conventional longitudinal reader configuration is typically implemented in perpendicular magnetic recording. FIG. 1 illustrates a conventional longitudinal reader 11. The reader 11 includes a first magnetic shield 13 and a second magnetic shield 15, each spaced apart from a reader 17. The first and second magnetic shields 13 and 15 have a shield-to-shield spacing SS. The reader 17 has a stripe height H and a track thickness T. The track-width of the reader 17 is not shown, but is generally perpendicular to the track thickness T.
It has been determined that the conventional longitudinal reader configuration does not optimally suit perpendicular magnetic recording, especially at high recording densities. One reason is that conventional longitudinal reader configurations implemented in perpendicular magnetic recording are going to have significant non-desirable side reading. Side reading generally refers to the reader reading or sensing magnetic fields in tracks adjacent to a track upon which a read operation is being performed.
The purpose of the magnetic shields, such as the magnetic shields 13 and 15 for the conventional longitudinal reader 11 illustrated in FIG. 1, is to define the linear resolution of the reader. In other words, the resolution of the reader in an xe2x80x9calong-the-trackxe2x80x9d direction is roughly determined by the shield-to-shield spacing SS of the magnetic shields 13 and 15. However, for the conventional longitudinal reader 11, there is not generally any effective xe2x80x9cshield-to-shieldxe2x80x9d boundary in an xe2x80x9cacross-the-trackxe2x80x9d direction to prevent the undesirable side reading. The side reading becomes even more problematic when the conventional longitudinal reader 11 is implemented in a perpendicular magnetic recording system because of enhancement of the side reading by use of the soft magnetic underlayer in the perpendicular recording medium.
Another disadvantage of using a conventional longitudinal reader for perpendicular magnetic recording is a relatively degraded resolution of the reader if it is used with perpendicular media. Resolution of a reader is generally defined by the smallest bit size the reader is capable of distinguishing. Therefore, the better the resolution of the reader, the smaller the bit size the reader can distinguish. Consequently, the better the resolution of the reader, the larger the data density than can be read back from a recording medium.
It has been determined that another fundamental disadvantage of implementing a conventional longitudinal reader in perpendicular magnetic recording is the fundamental difference of waveforms generated in the perpendicular and longitudinal recording modes. For example, FIG. 2 schematically illustrates calculated signal responses by the same longitudinal reader, such as reader 11, from a longitudinal 19 and a perpendicular 21 media single transition, wherein a single transition corresponds to the time instance of zero. The calculations were based on the reciprocity principle using a commercial three-dimensional boundary element field solver to calculate the sensitivity functions. From FIG. 2, it can be determined that the longitudinal response 19 is relatively more local than the perpendicular response 21. In other words, the longitudinal signal 19 comes only from the transition while the perpendicular signal 21 spreads significantly from the transition.
FIG. 3 illustrates calculated sensitivity fields used in the reciprocity principle for the longitudinal and perpendicular modes illustrated in FIG. 2. More specifically, FIG. 3 illustrates a longitudinal component 23 (Hx) and a perpendicular component 25 (Hy) of the sensitivity field for the longitudinal reader at the vicinity of the recording layer. It can be seen that the sensitivity function of the longitudinal reader has a bi-polar shape for the longitudinal component 23 and a mono-polar shape for the perpendicular component 25. In other words, the bi-polar shape of the longitudinal component 23 effectively provides a xe2x80x9cdifferentiatingxe2x80x9d of the signal at the transition, and consequently avoids reading far from the transition. Therefore, it would be advantageous to provide a perpendicular read head design with the sensitivity field of the bi-polar shape to reduce or eliminate side reading by the effective xe2x80x9cdifferentiationxe2x80x9d. Ideally, for the purpose of keeping the same signal xe2x80x9cchannelxe2x80x9d properties, i.e. a shape of the waveform of the playback signal directly sensed by a reader and thus methods to analyze this signal, the shapes of the perpendicular and the in-plane field components should be interchanged when transitioned from longitudinal to perpendicular recording.
There is identified, therefore, a need for a read head for a perpendicular magnetic recording system which overcomes disadvantages, limitations, or shortcomings of known read heads, and in particular conventional longitudinal readers, that may be used in a perpendicular magnetic recording system.
Embodiments of the invention meet the identified need, as well as other needs, as will be more fully understood following a review of this specification and drawings.
In accordance with an aspect of the invention, a read head for perpendicular magnetic recording includes a read element and means for magnetically shielding the read element to reduce side reading. The means for magnetically shielding the read element may include a magnetic shield spaced apart from the read element and at least partially surrounding the read element at an air-bearing surface of the read element. The ratio of an air-bearing surface area of the magnetic shield to an air-bearing surface area of the read element is from about 1:1 to about 40:1. In addition, the magnetic shield may be spaced apart from the read element a distance from about 10 nm to about 50 nm.
In accordance with an additional aspect of the invention, a read head for perpendicular magnetic recording comprises a read element and a magnetic shield spaced apart from the read element. The ratio of an air-bearing surface area of the magnetic shield to an air-bearing area of the read element is from about 1:1 to about 40:1. The magnetic shield at least partially surrounds the read element at an air-bearing surface of the read element.
In accordance with yet another aspect of the invention, a magnetic disc drive storage system includes a housing, a perpendicular magnetic storage medium positioned in the housing and a read head for perpendicular magnetic recording positioned adjacent the perpendicular magnetic storage medium. The read head of the magnetic disc drive storage system is constructed in accordance with the invention as described herein.